Over the years, general purpose railway boxcars have progressed from relatively simple wooden structures mounted on flat cars to more elaborate arrangements including insulated walls and custom designed refrigeration equipment. Various types of insulated boxcars are presently manufactured and used. A typical insulated boxcar includes an enclosed structure mounted on a railway car underframe. The enclosed structure generally includes a floor assembly, a pair of side walls, a pair of end walls and a roof. The side walls, end walls and roof often have an outer shell, one or more layers of insulation and interior paneling.
The outer shell of many railway boxcars often has an exterior surface formed from various types of metal such as steel or aluminum. The interior paneling is often formed from wood and/or metal as desired for the specific application. For some applications the interior paneling has been formed from fiber reinforced plastic (FRP). Various types of sliding doors including plug type doors are generally provided on each side of conventional boxcars for loading and unloading freight. Conventional boxcars may be assembled from various pieces of wood, steel and/or sheets of composite materials such as fiberglass reinforced plastic. Significant amounts of raw material, labor and time are often required to complete the manufacture and assembly of conventional boxcars.
The underframe for many boxcars include a center sill with a pair of end sills and a pair of side sills arranged in a generally rectangular configuration corresponding approximately with dimensions for the floor of the boxcar. Cross bearers and cross ties are provided to establish desired rigidity and strength for the associated railway car underframe. A plurality of longitudinal stringers are also often provided on each side of the center sill to support the floor of a boxcar. Examples of such railway car underframes are shown in U.S. Pat. Nos. 2,783,718 and 3,266,441.
Traditionally, refrigerated boxcars often have less inside height than desired for many types of lading and a relatively short interior length. Heat transfer rates for conventional insulated boxcars and refrigerated boxcars are often much greater than desired. Therefore, refrigeration systems associated with such boxcars must be relatively large to maintain desired temperatures while shipping perishable lading.
A wide variety of composite materials have been used to form railway cars and particular boxcars. U.S. Pat. No. 6,092,472 entitled “Composite Box Structure For A Railway Car” and U.S. Pat. No. 6,138,580 entitled “Temperature Controlled Composite Boxcar” show some examples. One example of a composite roof for a railway car is shown in U.S. Pat. No. 5,988,074 entitled “Composite Roof for a Railway Car”.